Answer:
They are combination structures made up of solid, and shell structures.
Explanation:
Thinking of a lunch pack which is shaped as a solid bag made up of different compartments to hold food, what comes to mind are;
1. The solid structure: This is seen in the form of the bag which has solid makeup.
2. The shell structure: This is seen in the different compartments holding the different types of foods. Shell structures are usually in the form of containers made to hold something in.
Answer: (a) 9.00 Mega Newtons or 9.00 * 10^6 N
(b) 17.1 m
Explanation: The length of wall under the surface can be given by

The average pressure on the surface of the wall is the pressure at the centeroid of the equilateral triangular block which can be then be calculated by multiplying it with the Plate Area which will provide us with the Resultant force.
![F(resultant) = Pavg ( A) = (Patm + \rho g h c)*A \\= [100000 N/m^2 + (1000 kg/m^3 * 9.81 m/s^2 * 25m/2)]* (140*25m/sin60)\\= 8.997*10^8 N \\= 9.0*10^8 N](https://tex.z-dn.net/?f=F%28resultant%29%20%3D%20Pavg%20%28%20A%29%20%3D%20%28Patm%20%2B%20%20%5Crho%20g%20h%20c%29%2AA%20%5C%5C%3D%20%5B100000%20N%2Fm%5E2%20%2B%20%281000%20kg%2Fm%5E3%20%2A%209.81%20m%2Fs%5E2%20%2A%2025m%2F2%29%5D%2A%20%28140%2A25m%2Fsin60%29%5C%5C%3D%208.997%2A10%5E8%20N%20%5C%5C%3D%209.0%2A10%5E8%20N)
Noting from the Bernoulli equation that

From the second image attached the distance of the pressure center from the free surface of the water along the surface of the wall is given by:
Substituting the values gives us the the distance of the surface to be equal to = 17.1 m
In an alternating current (AC) circuit the two poles alternate between negative and positive and the direction of the current (electron flow) reverses periodically.